February 28, 2014

4.2 kiloyear event and the demise of Indus Valley megacities

From the paper:

The 4.2 ka aridification event is regarded as one of the most severe climatic changes in the Holocene, and affected several Early Bronze Age populations from the Aegean to the ancient Near East (Cullen et al., 2000; Weiss and Brad- ley, 2001). This study demonstrates that the cli- mate changes at that time extended to the plains of northwestern India. The Kotla Dahar record alone cannot fully explain the role of climate change in the cultural evolution of the Indus civilization. The Indus settlements spanned a diverse range of environmental and ecological zones (Wright, 2010; Petrie, 2013); therefore, correlation of evidence for climate change and the decline of Indus urbanism requires a comprehensive assessment of the relationship between settlement and climate across a sub- stantial area (Weiss and Bradley, 2001; Petrie, 2013). The impact of the abrupt climate event in India and West Asia records, and that observed at Kotla Dahar, on settled life in the Indus region warrants further investigation.

Plato (or rather the Egyptian priest speaking through Plato) may have been the first one to note the differential survival of people as a result of natural catastrophes. It is hard to imagine that such an extreme event would not unbalance agricultural economies leading to famine and also endanger the supply systems on which early cities were based. The failure of cities would in turn lead to a failure of governing elites centered on them and a power vacuum which new elites (armed with bronze weapons at this time) might take advantage of. Climate may have ended the Bronze Age civilization itself 1000 years later.

Climate change has been suggested as a possible cause for the decline of urban centers of the Indus Civilization ∼4000 yr ago, but extant paleoclimatic evidence has been derived from locations well outside the distribution of Indus settlements. Here we report an oxygen isotope record of gastropod aragonite (δ18Oa) from Holocene sediments of paleolake Kotla Dahar (Haryana, India), which is adjacent to Indus settlements and documents Indian summer monsoon (ISM) variability for the past 6.5 k.y. A 4‰ increase in δ18Oa occurred at ca. 4.1 ka marking a peak in the evaporation/precipitation ratio in the lake catchment related to weakening of the ISM. Although dating uncertainty exists in both climate and archaeological records, the drought event 4.1 ka on the northwestern Indian plains is within the radiocarbon age range for the beginning of Indus de-urbanization, suggesting that climate may have played a role in the Indus cultural transformation.

The 4.1 kiloyear event was the main trigger of Indo-European expansion and regime changes in the Eastern Mediterranian. It corresponds to the rise of the Mycenean Greeks, and the sudden appearance of cremation on the Pannonian plain and along some locations on the mid-Danube River basin around 4000 BP. The Tocharians appear in the Tarim Basin around 3811 BP. A contemporaneous written historical record from a trading Mesopotamian trading colony in S. Central Asia Minor states that the Hittites conquered their second city-state in 3765 BP and that before then the Hittites ruled only a single city. There was anarchy in the Akkadian empire for twenty-four years from 2192 BCE to 2168 BCE, followed by 14 years of consolidated Akkadian rule after which the Akkadian empire collapsed in 2154 BCE in the wake of an invasion from the Gutian barbarians from the Zagros Mountains. As Wikipedia explains:"Cuneiform sources suggest that the Gutians' administration showed little concern for maintaining agriculture . . . they reputedly released all farm animals to roam about Mesopotamia freely, and soon brought about famine and rocketing grain prices. The decline coincided with severe drought, possibly connected with climatic changes reaching all across the area from Egypt to Greece. The Sumerian king Ur-Nammu (2112–2095 BC) cleared the Gutians from Mesopotamia during his reign.It has recently been suggested that the regional decline at the end of the Akkadian period (and of the First Intermediary Period that followed the Ancient Egyptian Old Kingdom) was associated with rapidly increasing aridity, and failing rainfall in the region of the Ancient Near East, caused by a global centennial-scale drought. H. Weiss et al. have shown "Archaeological and soil-stratigraphic data define the origin, growth, and collapse of Subir, the third millennium rain-fed agriculture civilization of northern Mesopotamia on the Habur Plains of Syria. At 2200 B. C., a marked increase in aridity and wind circulation, subsequent to a volcanic eruption, induced a considerable degradation of land-use conditions. After four centuries of urban life, this abrupt climatic change evidently caused abandonment of Tell Leilan, regional desertion, and collapse of the Akkadian empire based in southern Mesopotamia. Synchronous collapse in adjacent regions suggests that the impact of the abrupt climatic change was extensive." Peter B. deMenocal, has shown there was an influence of the North Atlantic Oscillation on the stream flow of the Tigris and Euphrates at this time, which led to the collapse of the Akkadian Empire"....Tell Leilan in Northern Mesopotamia...was abandoned soon after the city's massive walls were constructed, its temple rebuilt and its grain production reorganised. The debris, dust and sand that followed show no trace of human activity. Soil samples show fine wind-blown sand, no trace of earthworm activity, reduced rainfall and indications of a drier and windier climate.... [S]keleton-thin sheep and cattle died of drought, and up to 28,000 people abandoned the site, seeking wetter areas elsewhere. Tell Brak shrank in size by 75%. Trade collapsed. Nomadic herders such as the Amorites moved herds closer to reliable water suppliers, bringing them into conflict with Akkadian populations. This climate-induced collapse seems to have affected the whole of the Middle East, and to have coincided with the collapse of the Egyptian Old Kingdom. This collapse of rain-fed agriculture in the Upper Country meant the loss to southern Mesopotamia of the agrarian subsidies which had kept the Akkadian Empire solvent. Water levels within the Tigris and Euphrates fell 1.5 metres beneath the level of 2600 BC, and although they stabilised for a time during the following Ur III period[.]"

Recent studies have pointed to violence and disease as the causes for the demise of IVC. We can now say that there was increase in disease and incidents of violence among the population especially in the lower strata because of food and resource shortages that resulted from frequent drought conditions that occurred over 200 years

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